1. Field of the Invention
The invention relates to a wall thickness measuring device for pipes, cable casings and the like, more particularly of extruded plastics, having a measuring head which is connected to measuring and supply leads and is mounted to reverse around an opening of passage for the pipe to be measured on a guide attached to a frame having the opening of passage.
2. Discussion of Prior Art
In known wall thickness measuring devices operating on the ultrasonics principle the sensor is forced against the pipe by means of a pressure-operated approach device, using a probe-to-specimen contact medium, more particularly water. Since due to the required measurement of the wall thickness the measuring head is mounted to be reversed over the whole periphery, the measuring and supply leads extend fairly freely. One prior art device provides for the leads a winding frame which can be moved reversibly together with the measuring head. However, the winding frame guides the leads only in the immediate zone of the opening of passage, while the leads otherwise extend freely (Reprint from the Journal: "Kunststoffe, 77, 1987/9, Published by Carl Hanser Verlag, Munich; "Automatic ultrasonics wall thickness measurement in pipe extrusion" by J. Orzechowski, Bad Oeynhausen; Company Publication of Battenfeld Extrusionstechnik GmbH "Automation of pipe extrusion", pages 10 and 11).
In another wall thickness measuring device of the kind specified the measuring head, which has an oscillator, is borne by a rotably mounted hollow shaft which also bears a primary winding and a secondary winding of high frequency transformers. The oscillator is connected to the windings disposed on the hollow shaft via cables laid in the measuring head and in bores in the hollow shaft. Unlike the first-mentioned prior art, no measuring and supply leads are provided to connect the movable measuring head to a fixed measuring device (German AS 1 239 484).